You may think the Chapman Brothers produce pretentious, adolescent toss, or you may have seen something imaginative in their Hell. But you can't deny their art is visceral, bold and tackles big themes - unlike the half-cock selection of artists for this year's Turner prize, and the debate initiated by Kim Howells, which has no complexity or grandeur. The Chapmans' art is juicy rather than dry. It may be crap, it may be derivative - Jeff Koons should probably sue - but it doesn't fall into a neat division of concept versus craft. They laugh at the idea that craft has an inherent moral integrity by mastering a number of traditional arts and crafts - drawing and engraving, the diorama and now wood carving - without claiming to be doing anything so crass as express themselves.

Their latest wheeze is to exhibit the Chapman Family Collection, a unique gathering of "rare ethnographic and reliquary fetish objects" that the Chapman family has accumulated over the years. In a darkened, hushed hall, pools of light illuminate painted wooden masks, stuck through with fetish nails, decorated with shells and goats' heads. They appear authentic until you notice the McDonald's logo everywhere. A burger as a primeval deity; a cult statue with the evil clown face of Ronald McDonald; a horned devil out of some dreadful Hammer film in which Roy Castle is the victim of a voodoo curse.

It is all genuinely offensive. Western modernism exploited tribal art, tearing it out of context to make it the vessel of primitivism. Making your own pastiche "primitive" art and mutating it into an image of capitalism - I think Marx's theory of commodity fetishism is in here somewhere - is going to have a lot of people's hackles rising. Mine included. But then, the museum displays that this exhibition parodies decontextualise and make a travesty of ethnographic art anyway; we see masks intended to be worn in specific social contexts reduced to aesthetic objects. Surely it is this that creates kitsch. The Chapmans are just the messengers.

This is the kind of art the Turner prize ought to be showing - it would create a row not about the tedious issue of conceptual art good or bad, but about colonialism, capitalism, racism, the responsibilities of art and the evil of banality. At the very least, the Chapmans are superior bullshit artists.